Problem: If $a + b + c = 9$ and $x + y + z = -9$, what is $-4x + 6c + 6a - 4z + 6b - 4y$ ?
Solution: $= 6a + 6b + 6c - 4x - 4y - 4z$ $= (6) \cdot (a + b + c) + (-4) \cdot (x + y + z)$ $= (6) \cdot (9) + (-4) \cdot (-9)$ $= 54 + 36$ $= 90$